Rauner, a private equity specialist who has put his own net worth at more than $500 million, has only offered voters a narrow glimpse into his personal finances to date. The Republican nominee has released three years of basic tax forms without the detailed supporting documents such as schedules that many other candidates often make public.

Asked if Rauner should release his income tax returns, complete with the schedules, Emanuel pointed to the fact that he repeatedly has released his own taxes. The mayor said he released his taxes while running for congress and for mayor, including tax returns from when he served as White House chief of staff to President Barack Obama. Emanuel indicated Rauner should do the same, although he did not mention him by name.

“Running for office and releasing your tax returns is like a rite of passage. You have to do it,” said Emanuel, who has released his tax returns complete with schedules. “I have always made them public, and they speak to what I think is the right thing to do and it's a rite of passage when you’re running for office, especially chief executive.”

Emanuel is threading a needle when it comes to Rauner. The two have vacationed together. And they did a business deal during Emanuel’s brief stint as an investment banker. Emanuel helped broker a deal in which Rauner’s GTCR bought alarm company SecurityLink for $479 million from SBC. GTCR flipped it to another buyer six months later for a price of $1 billion.

Rauner also has served as an unofficial adviser to the mayor and has said he regularly spoke with Emanuel. One key area of agreement is support for charter schools and criticism of the Chicago Teachers Union.

Chuck Berman

Mayor Rahm Emanuel, seen here at an event about expanded air conditioning for public schools today, said Republican governor candidate Bruce Rauner should release his tax returns.

Mayor Rahm Emanuel, seen here at an event about expanded air conditioning for public schools today, said Republican governor candidate Bruce Rauner should release his tax returns. (Chuck Berman)

For his part, Emanuel has publicly endorsed Quinn, a fellow Democrat, for governor.

Last week at the State Fair in Springfield, Rauner showed no signs he would bow to Quinn's call to release a full set of income tax returns, including schedules that would detail his multiple sources of income. The last tax statements Rauner made public showed he made $53 million in one year. The Republican candidate said Quinn is trying to throw a “bunch of mud in the air to try to create a diversion.”

The Tribune reported last month that IRS data shows Rauner is one of the 11,000 richest tax filers in the nation, and a review of what tax documents the GOP hopeful did release showed most of the millions he made in recent years was taxed at 15 percent – less than half the top federal rate for the wealthy.

Rauner’s combined federal tax bill was $20.7 million from 2010 through 2012. Quinn’s, according to his tax returns for those years, totaled about $106,600 on income of about $568,000, giving the governor an effective tax rate of 18.8 percent.

Rauner has said he would not be releasing additional tax documents beyond the 1040s he has made public. Tax experts consulted by the Tribune last month said such a broader disclosure would almost certainly shed light on the strategies used to minimize Rauner’s tax bill.

Emanuel's remarks came during an appearance at Patrick Henry Elementary School on the Northwest Side where he announced the completion of additional air conditioning at 57 schools.